High speed reciprocating ram pump



Patented Aug. 19, 1941 UNITED STATES PATENT OFFICE 2,253,152 HIGH SPEEDRECIPROCATING RAM PUMP Frank Hathorn Towler and John Maurice Towler,

Yorkshire, England Application August 1, i938, Serial No. 222,518 InGreat Britain August 16, 1937 1 Claim.

to dispense with the necessity of a by-pass and a relief valve but insuch a way that the pump continues to run but ceases to discharge liquidfrom the pump chamber when'the predetermined maximum pressure above thedischarge valve is attained but if the pressure falls due to leakage thepump automatically makes up the leakage so that in the case for instanceof, its application to a hydraulic baling press, positive stops maysafely be used at the limit of movement of the press rams, and the pumpwill maintain the bale under pressure until it has been securely wired.

ner that the displacement member continues to displace the imprisonedliquid without causing any of said imprisoned liquid to be discharged.

The attainment of a similar object has been attempted by placing avessel full of liquid in permanent communication with the cylinder orchamber of an ordinary hydraulic pump the cat pacity thus produced beingpredetermined so that the displacement of the pump piston or ram doesnot produce more than a certain predetermined pressure within the pumpcylinder.

In this prior proposal the connection between the vessel and the pumpchamber consisted of a comparatively long and small bore pipe having aright-angled bend in. its length.

From experiments we have made with reciproeating ram pumps having such apermanently connected vessel we have proved that the arrangementheretofore proposed is impracticable for a pump which is required todeliver a substantial quantity of liquid at low pressure. We have foundthat air, which is normally held in solu-- tion in the liquid, isliberated in the pump chamber when the pressure is released. The air soliberated finds its way into the horizontal portion of the restrictedpassage connecting the pump chamber to the said permanently connectedvessel. Then as the pressure against which the pump has to deliverincreases, the liquid in the pump chamber is compressed on the deliverystroke and passes along thehorizontal passage around the bend and sointo the said vessel, carrying the air with it. As the pressureincreases still further, this air is forced into solution with theliquid in the said permanently connected vessel, so that the resilienceof the liquid in the vessel is not seriousl affected and the pumpfunctions quite satisfactorily at maximum pressure. However, as soonasthe pressure against which the pump has to deliver is released, for morethan a momentary period, the air in the permanently connected vesselcomes out of solution and being trapped by the bend in the restrictedconnectingpassage it accumulates and forms an air cushion between thevessel and the pump chamber. This air cushion seriously reduces thevolumetric efficiency of the pump at low pressures and, as the aircontinues to accumulate in the passage, the pump becomes very nearlyineffective at low pressures. On the other hand, if the delivery passageof the pump is completely closed, the pump is usually suflicientlyeffective to build sufficient pressure in the said permanently connectedvessel to cause the air to go into solution again so that the pump againfunctions satisfactorily at maximum pressure. Thus, a pump, particularlya pump running at high speed, constructed as heretofore will functionsatisfactorily at maximum pressure, when the delivery of the pump iszero, or at pressures approaching the maximum when the delivery of thepump is comparatively insignificant, but the pump is practicallyineffective at low pressures.

W have found that for complete success the following conditions must befulfilled:

(1) The pump must operate at relatively high speeds and pressures so asto keep the size of the connected vessel reasonably small.

(2) The ram should, for preference, practically fill the pump chamber onthe-discharge strok so as almost completely to expel air or other gasliberated from the liquid during umpin (3) The connected vessel orchamber must be so situated in relation to the pump discharge valve thatany air in the vessel or chamber passes automatically and freely to thedischarge ilalve to be expelled by the pump. The air mayfpass to thedischarge valve in any one of" the following manners:

The use of an additional capacity in communi-- cation with the pumpchamber of a reciprocating ram pump for the purpose of controlling thepumps delivery is really impracticable in the case of slow speed pumps(60 to 150 R. P. M.) as owing to the very large displacement of suchpumps the additional capacity required would have to be relativelyenormous. For example in the case of a high speed pump running at 1500R. P. M. the 'ram displacement would be one tenth of that of anequivalent pump of the same power which ran at 150 R. P. M. Inconsequence the high speed pump would require an additional capacity onetenth that required by the slow speed pump assuming the pressure to bethe same in each case. Of course if the slow speed pump operates at alower pressure the size of the capacity will have to be correspondinglygreater.

While it is preferred that the pump ram shall almost completely fill thepump chamber on the discharge stroke this is not an absolute necessityfor success and for this reason it is not intended that the inventionshall be limited in this'respect but for best results it is advisablethat the condition shall obtain.

The present invention may, therefore, be said to consist broadly of apositive displacement pump of the high speed, high pressure type havinga vessel or chamber of predetermined capacity in communication with thepump chamber of the pump so as to increase the effective capacity ofsaid pump and in such relation to the pump discharge valve that any airin the vessel or chamber passes freely and. automatically and in asubstantially direct line to the discharge valve the capacity of saidvessel or chamber being such that liquid will automatically beimprisoned in the pump chamber capacity at a predetermined maximumpressure above the discharge valve and the displacement member or ramwill, at such maximum pressure, continue to displace the imprisonedliquid without causing any of said imprisoned liquid to be discharged.

In order that the invention may be clearly understood and carried intoeffect an embodiment showing the use of a closed vessel and anotherembodiment showing the use of a vessel through which the pump dischargeswill now be described by aid of the accompanying, somewhat diagrammaticdrawing in which:

Fig, l is a vertical longitudinal section through a high speedreciprocating ram pump having a closed vertically disposed vessel.

Fig. 2 is a similar view but illustrating the embodiment in which thedischarge valve is on the the kind described in the specification of ourco-- pending application No. 146,038 in which the pump ram almostcompletely fills the pump bore at the inner end of each stroke so asalmost completely to empty the pump bore of liquid before each suctionstroke.

In the drawing a indicates the pump body, b the pump ram, 0 the pumpchamber, d a mushroom type inlet valve situated at the inner end of thepump chamber so as to oppos the end of the ram, e the discharge valve, 1the large capacity chamber or vessel, 9 a straight and nonrestrictedpassage forming a communication between the interior of the vessel 1 andthe pump chamber h a ball or roller bearing mounted directly upon aneccentric i for imparting the inward or discharge stroke to the ram and1 pockets for th reception of springs for returning the ram on eachsuction stroke.

As shown the vessel j is vertical and below the pump chamber so that anyair released passes automatically and freely to the'discharge valve tobe expelled by the pump. In the, example illustrated in Figure 2 thevessel 1 may be above the pump chamber as any air released will becarried out of the pump at each discharge as will hereafter appear.

The example illustrated in Fig. 2 differs from the example illustratedin Fig, l in that the vessel I has an opening at its upper end which iscontrolled by the discharge valve of the pump.

By this means the liquid within the vessel is kept constantly changed asthe interior of the vessel constitutes a section of the dischargepassage through which the pump delivers during each discharge stroke.The collection 01' air within the vessel or the. restricted passage g isthus rendered impossible or at least negligible.

One of the principal uses of a pump according to the present inventionis in connection with a hydraulic baling or bundling press and tofurther explain the uses and operation of a pump according to thepresent invention particulars of such an application will now be givenin the following description.

In this application of the invention the hydraulic press is of normalconstruction excepting that the control valve has no mid-position, aswhen the bale is fully compressed the pump still continues to deliverliquid to the press cylinders, positive stops being provided to preventthe bale being compressed any further.

With a conventional pump the delivery of the pump would in this casehave to be by-passed or allowed to escape through a relief valve or thepump would have to be stopped.

In the present invention the pump is of the reciprocating ram typehaving one or more rams and each pump chamber is made of very largecapacity in relation to the pump ram displacement by the use of theaforesaid additional capacity vessel 1. Consequently, as the pressure inthe press cylinders increases the pump ram has first to compress theliquid in the pump chamber before lifting the pump delivery valve anddelivering the liquid to the press cylinder; and the amount of liquiddelivered at each stroke of the pump ram is reduced by the amount whichthe liquid has to be compressed in order to overcome the pressure in thepress cylinders and lift the delivery valve. The capacity of the-pumpchamber is so arranged in relation to the pump ram displacement that,when a predetermined maximum pressure is reached, the full inward strokeof the pump ram is only sufficient to compress the liquid to the.requisite pressure, but it is not sufllcient to lift the pump deliveryvalve against the pressure already attained in the press cylinders. Thatis to say that, as the pump ram continues to reciprocate, the liquid inthe pump chamber compresses and expands in unison; so that, with theexception of the frictional. losses, the energy expended in compressingthe liquid in the pump chamber is given back to the pump shaft on thereturn stroke when the liquid is allowed to expand. Thus, when the baleis fully compressed and the press table is prevented from compressing itany further because of the stops so provided, the predetermined maximumpressure is reached and the pump continues to run at full speed butwithout delivering any liquid into the cylinders, so that the powerrequired to'drive the pump at maximum pressure is only that .necessaryto overcome frictional losses; and,

since there is no delivery of liquid by the pump, there is no need toprovide a relief valve or other form of by-pass. It will be understood,further, that, as the pressure increases up to the maximum, the deliveryof the pump decreases proportionately, so that over a wide range ofpressure variation the lower required to drive the pump remainssubstantially constant. Thus, for sake of explanation we will take aspecific example. Let us imagine a single ram pump having a ramdisplacement each stroke of 0.35 cubic inch and we will assume that theliquid compresses 3 cubic inches per 1,000cubic inches volume per 1,000lbs. per sq. inch increase in pressure. If we make the pump chamber of16.67 cubicinches capacity, then the liquid in the chamber will compress0.05 cubic inch per'1,000 lbs. per sq; inch increase in pressure.Therefore, if we drive the pump at 1.000 R. P. M. it will deliver 350cubic inches per minute atno pressure at a theoretical pump 1horse-power of zero; 'and at 7,000 lbs. per sq. inch the liquid in thechamber will compress 0.35 cubic inch at each stroke of the ram, so thatthe open the communication between the pump chamber and the capacitychamber such valve being operated automatically. Further the capacity ofthe permanently connected vessel may be made variable by suitable meanssuch as by disposing within the same a longitudinally adjustable pistonso as to vary the maximum pressure at which the pump will give zerodelivery.

We claim:

In a reciprocating ram pump, in combination, a pump body, a bore in saidbody, a ram slidable within said bore, means for reciprocating said ram,a pump chamber. at the inner end of said bore, a supplementary chamberextending outwards from said pump body at right angles to said bore, astraight unrestricted passage 'at the inner end of the supplementarychamber and connecting the interior of said supplementary chamber withthe pump chamber, and a valve controlled discharge opening in line withand at the outer end of the supplementary chamber and opposing saidstraight unrestricted passage whereby the liquid being pumped is causedto pass through said supplementary chamber, the arrangement being suchthat the supplementary chamber provides, with the pump chamber, a

capacity for retaining a body of liquid of such theoretical pumphorse-power will again be zero;

but between 2,000 lbs. per sq. inch and 5,000 lbs. per sq. inch thetheoretical pump horse-power varies from 1.25 horse-power to 1.5horse-power and back again to 1.25 horse-power at 5,000 lbs. per sq.inch and the pump delivery varies from 250 cubic inches per minute at2,000 lbs.per sq. inch to 100 cubic inches per minute at 5,000- lbs.

per sq. inch. The above figures are approximate and no allowance hasbeen made for friction or loss of volumetric eiiiciency in the pump. Itwill be understood that this invention may be applied to a high speedreciprocatlng ram pump such as predetermined volume that the same iscompressible by the ram to'cause the delivery of the a pump to decreaseproportionately to increase of a pressure above the discharge valve"until a predetermined maximum pressureis reached, whilst free airwithin said body of liquid passes freely and in a substantially directline outwards through the supplementary chamber to the discharge. valvefor removal with the liquid being pumped.

FRANK HATHORN TOWLER.

JOHN MAURICE TQWLER.

